ABSTRACT Cochlear implants s(CIs) provide hearing to deaf individuals by electrically stimulating the auditory nerve. Bilateral implantation has become a standard treatment in many countries, in an attempt to provide patients with auditory cues needed to segregate speech from noise and localize sounds. Despite notable benefits when listening with bilateral vs. unilateral CIs, most patients continue to perform significantly worse than normal hearing (NH) listeners. The most likely reason is the lack of synchronization of stimulation in the right and left ears. Binaural functioning in NH depends on neural coding of interaural differences in time (ITD) and level (ILD), and ILDs alone are not sufficient for producing excellent performance. Although today?s clinical processors are designed to maximize speech understanding, they do not present binaural cues to the electrode arrays in a reliable and suitable manner. We propose to investigate means for overcoming these limitations, using research interfaces that control ITDs and ILDs, with novel signal processing. Aim 1 will systematically investigate the effectiveness of novel hybrid-rate multi-channel stimulation aimed at preserving both binaural sensitivity and speech understanding. We reason that strategies that combine low-rate with high- rate stimulation engage neural mechanisms that encode both interaural timing cues (at low-rate stimulation) and envelope speech cues (at high-rate stimulation). In addition to binaural psychophysics, we will assess monaural pulse rate sensitivity as a first step towards independent assessment of neural health at each of the electrodes used in binaural stimulation. In NH listeners we will conduct novel experiments on how different hybrid rate configurations can affect overall binaural sensitivity when cues are distributed along the multiple frequency regions. The ultimate goal is to work with engineering teams that can implement these strategies in clinically fit CI processors. If successful, this approach will help to close a gap in performance that exists between CI users and NH listeners. Aim 2 will use a unique approach that measures pupil dilation (to quantify listening effort) and speech intelligibility concurrently. We will compare performance in conditions that have standard clinical listening vs. conditions aimed at improving speech intelligibility in noise and spatial release from masking. In the proposed work, our goal is to understand why patients seem to benefit from some listening strategies more than others, and more importantly to quantify the two aspects of benefit: improvement in speech intelligibility and reduced listening effort. Proposed studies are aimed at gaining insight into dimensions of real-world listening that are poorly understood. The ultimate goal is to identify binaural strategies that yield improvements across patients, so that future work can implement those strategies in a portable clinical device. In NH listeners, our proposed studies will be the first to investigate the importance of binaural cues for understanding speech in noise and listening effort.